As is well known there exist numerous methods of treating municipal sewage to separate it into an effluent portion and a sludge portion. In one treatment process of this type, liquid sewage is pumped into generally rectangular filtration beds. These filtration beds are bounded by cement retaining walls and contain layers of gravel overlain by a depth of sand, with underlying drain outlets. In the treatment process, such filtration beds are covered with liquid sewage to a depth of between 12 to 16 inches. The liquid portion is gravitationally filtered through the sand and gravel and is removed from beneath the gravel through the outlets for further processing. The residue or sludge remains atop the sand and gradually dries into a cake of solid waste approximately two inches thick.
When the sludge has dried it must be removed from the filtration bed so that the treatment process can be repeated. A minimum amount of sand should be removed with the sludge for obvious economic and efficiency reasons. Current practice is to remove the sludge manually by using a crew of several workmen with pitchforks and shovels. Therefore it is clear that the removal aspect of the treatment process is a labor and time-consuming operation.
Mechanical solutions to eliminate the labor intensive aspects of removal of the sludge from the bed have been attempted. In particular removal of the sludge using a landscape rake of the type known as a "ROCK HOUND".RTM. manufactured by KEM Enterprises, Inc. was attempted. The results were not satisfactory because the consistency of the sludge and the underlying sand was such that movement of the device over the sludge caused the sludge to buckle and accumulate at the front of the device. Thus, the landscape rake quickly became little more than a plow or scraper.